The pigment of human skin or hair functions to protect the skin or hair from the deleterious effects of sunlight, particularly UV light. Persons lacking this pigment are very sensitive to sunlight, so that they are more likely to get burned. Also, there is a high likelihood of occurrence of skin cancer, even at young ages. It is known that short-wavelength UV rays (290-320 nm) and carcinogenic substances form harmful radicals, for example, oxygen radicals, on the skin, and such oxygen radicals attack skin cells to cause skin aging. The main function of melanin is to scavenge such harmful radicals, thus protecting the skin from damage caused by such harmful radicals. Accordingly, people having plenty of melanin have an effective defense system capable of protecting the skin from physical or chemical toxic substances. Factors promoting the production of melanin include, in addition to sunlight (UV light), estrogens and prostaglandins. Melanin is produced by melanocytes after the conversion of tyrosine to dopachrome through the action of the enzyme tyrosinase, followed by complex oxidation and condensation reactions. The produced melanin are transferred into skin cells and lost with epidermal peeling. This melanin production process is a naturally occurring phenomenon, and in a normal human skin, the overproduction of melanin does not occur. However, when the skin responds to external stimuli, for example, UV light, environmental pollutants or stresses, the overproduction of melanin will occur. When the overproduced melanin remains in the skin without being discharged out of the skin, pigmentation will occur. Among the above-described external stimuli, UV light is the greatest source stimulating melanin biosynthesis and can influence various processes associated with melanin production. That is, UV light acts as an important factor which induces the overproduction of melanin by promoting the activity of melanocytes, the secretion of hormones stimulating melanin biosynthesis, the oxidation of melanin, or the activity of tyrosinase.
The greatest characteristic of this melanin production mechanism is that only one enzyme, tyrosinase, is involved in the melanin production mechanism. When the tyrosinase activity is inhibited to prevent the production of melanin, a skin-whitening effect can be expected.
In the prior art, it is known to use ascorbic acid as a whitening substance (Japanese Patent Laid-Open Publication No. Hei 4-9320). However, ascorbic acid has a problem in that the activity thereof decreases with the passage of time, because the phase stability thereof in a formulation is poor. For this reason, various methods of stabilizing ascorbic acid with capsules or liposomes have recently been suggested, but a reliable stabilization method has not yet been suggested.
Also, it is known to use hydroquinone as another whitening substance (Japanese Patent Laid-Open Publication No. Hei 6-192062). Hydroquinone has excellent effects, but the use thereof in cosmetic products has been limited, because it is a carcinogenic substance.
Moreover, it is known to use kojic acid as still another whitening substance (Japanese Patent Laid-Open Publication No. Sho 56-7710). Kojic acid shows an excellent whitening effect due to an excellent ability to inhibit tyrosinase, but it has a problem in terms of the stability thereof in a formulation and was recently reported to be a carcinogenic substance.
In addition, it is known to use arbutin as still another whitening substance (Japanese Patent Laid-Open Publication No. 4-9315). Arbutin can be extracted from bearberries growing in alpine belts or can be obtained through synthesis. Also, it has a proven ability to inhibit tyrosinase, like kojic acid. However, arbutin has a structure in which sugar binds to hydroquinone, and it has a problem in that, when it is applied in cosmetic products, the sugar is separated by skin enzymes, such that skin irritation is induced by the hydroquinone.
Various patents and scientific articles are referred to throughout the specification. The disclosure of the cited patents and scientific articles is incorporated herein by reference in its entirety, such that the general knowledge of the technical field to which the present invention pertains and the content of the present invention are more clearly explained.